1. Field of the Invention
The invention relates to a method and circuit arrangement for determining the rotor position of an electronically commutated motor (EC motor). Methods of this kind, which are required for a controlled run-up of EC motors from the standstill state with maximum moment, are basically known. In this connection, the detection of the rotor position is carried out either with the aid of rotation angle sensors or alternatively without such sensors, through the use of magnetic machine effects.
2. Description of the Prior Art
For machines with a magnetically asymmetrical or symmetrical rotor, DE 101 62 380 A has disclosed determining the position of the rotor in the standstill state of the machine. In this instance, the measurement is carried out using saturation effects in the rotor iron so that over a full rotation of the rotor, the stator phases are acted on cyclically by a number of current pulses that corresponds to twice the number of stator phases, which pulses are respectively offset from one another by the same angle. The rise times of the current pulses, which occur in accordance with the degree of saturation of the respective rotor section are then used to determine the rotor position in the standstill state of the motor. Such a method requires a large number of powerful current pulses for the measurement, which causes unwanted magnetic noise, movements of the motor shaft, and a delay in the starting of the motor.
In addition, the prior art (German patent application 102 005 007 995.4) already includes the proposal of determining the position of the rotor of an EC motor in two successive steps in that in order to ascertain the position of the d-axis, the stator of an EC motor with a magnetically asymmetrical rotor is initially excited with current pulses that do not result in saturation effects in the rotor, and in this case, measuring the magnitude of the current that occurs. Then a stator phase that can be associated with the d-axis of the rotor is acted on with current pulses, which produce a saturation of the iron in the rotor, in order to determine the north/south orientation of the rotor. In both measurement procedures, the potential is measured on the one hand, at the winding star point of the stator and on the other hand, at a summation point of the phase voltages generated by means of resistances and is used as a criterion for the magnetic concatenation between the stator and the rotor of the motor. To this end, the winding star point of the stator must be led out and made accessible, thus limiting the usability of the motor. In addition, the detection of potentials increases the circuitry complexity of the arrangement since an analog/digital conversion is required in the control unit. Because of the required magnitude and duration of the individual phase current supplies, the current in the stator windings is reversed during the measuring procedure in order to achieve a quasi-stationary state of the rotor. This results in a relatively long measurement duration.
It is also known to determine the position of the rotor without the use of rotation angle sensors after the motor is started, based on the induced revolving field voltage in the respective unpowered phases. This method, however, only permits a reliable conclusion to be drawn about the rotor position after the motor has reached a certain minimum speed.